noun. a rare STD in which the genitals suddenly explode without further notifications, usually during the day when no one expects it to happen

Teacher: Tell me class, using the law of sines, what is the angle of A?
Student: Well, since angle B is 46 degrees, side b is 23 units, and side a is 13 units, we can say that...*balls explode*
Teacher: Oh my darkness! He suffered from genital combustion!

A rare sexually transmitted disease whose main symptom is the spontaneous combustion of one's genitals. In some cases, this can be more dangerous to those around one with Genital Combustion. For example, a woman with Genital Combustion may, in some cases, create a flamethrower with her vagina, injuring those nearby. A man with Genital Combustion will, in most cases, have his dick catch fire and in seconds be consumed by flames where he will then be sent to the underworld to await eternal punishment. There is no cure as of yet for Genital Combustion, but our nation's top minds are spending the taxpayer's money to find one. To avoid catching Genital Combustion, it is advised that you stay away from poorly cleaned genitalia. Also, if the genitals smell anything like roasted almonds, it is advised that sexual activity not be performed. For more information on Genital Combustion, light you genitals on fire and tell us how it feels.